Welcome to NORAC
The North Okanagan Radio Amateur Club

Nav view search

Navigation

Search

Search ...

GUIDE - DXing on the VHF and UHF Bands (TechNet016)

DXing on the VHF and UHF bands

Although DXing or making long distance contacts is traditionally found on the HF bands, an active and growing community enjoys DXing on the bands above 30 MHz. This activity also increases when the solar cycle is lower like we’re currently experiencing. The excitement of extending your station’s capability to these bands is being shared by more hams than ever before. The explosion in popularity of VHF/UHF DXing is similar to the explosion of HF DX enthusiasm in the 1960s, when top-quality equipment became available to the average ham. These days, the latest generation of all-band HF/VHF/UHF radio equipment puts top-notch higher frequency DXing on the shack desktop.

With the exception of the 6 meter band (known as the magic band because of its sudden and dramatic openings for distant stations), these higher frequencies usually don’t support the kind of long-distance, transoceanic contact that’s common on HF, because the ionosphere can’t reflect those signals. VHF/UHF DXers look for contacts by using different methods of propagation.

The VHF and UHF bands have undeserved reputations for being limited to line-of-sight contacts because of the limitations of previous generations of relatively insensitive equipment and the prevalence of FM, which takes considerably more signal strength to provide signal quality equivalent to single sideband (SSB) and Morse code transmissions. By taking advantage of well-known modes of radio propagation, you can extend your VHF and UHF range dramatically beyond the horizon.

Finding and working VHF and UHF DX

As on the HF bands, you find DX stations at the lowest frequencies on the band in the so-called weak signal segments. On the 6 meter band, for example, 50.0–50.3 MHz — a 300 kHz segment as large as most HF bands — is where the Morse code and SSB calling frequencies are located. Similar segments exist on all VHF and UHF bands right through the lower microwave frequencies.

When you’re DXing on VHF or UHF, stay close to these calling frequencies, or set your radio to scan across the low end of the band and leave the radio on. Propagation between widely separated points is often short-lived. If you wait for somebody to call you or e-mail you with news about a DX station, you’re probably going to miss the boat. Set your squelch control (squelch mutes the receiver unless a signal exceeds a preset level) so that the radio is barely quieted. If anything shows up on the frequency, the radio springs to life. This way, you (and whoever else is in earshot) don’t have to listen to continuous receiver hiss and random noise.

For this type of DXing, it’s recommended to use a small beam antenna. A beam antenna is easy to build, is relatively small compared with HF antennas, and is a terrific homebrew project. Mount the antenna for horizontal polarization, with the antenna elements parallel to the ground. You should be able to point the antenna in any horizontal direction, because signals may appear from nearly any direction at any time. Adding a cheap TV antenna rotator would allow you to change the direction of the beam without having to climb up on your roof or tower.

To find out more about VHF/UHF propagation, join one of the many VHF/UHF contest clubs. These helpful, energetic groups make a lot of expertise available through their websites and at meetings. Another strong community of VHF/UHF DXers is in nearly constant communication worldwide at www.dxworld.com.

Sporadic E

The term sporadic E refers to an interesting property of one of the lower ionospheric layers: the E layer. Somewhere around 65 to 70 miles above the Earth, illumination of the E layer by the Sun produces small, highly ionized regions that are reflective to radio waves — so reflective that they can reflect signals from the 6 meter, 2 meter, 1.25 meter, and (rarely) 70 cm bands back to Earth. These regions, which drift around over the Earth’s surface, usually don’t last more than an hour or two. While they’re available, though, hams can use them as big radio reflectors. Their unpredictable nature has led to the name Sporadic E.

Sporadic E (or Es) propagation occurs throughout the year but is most common in the early summer months and the winter. When sporadic E is present, signals appear to rise out of the noise over a few seconds as the ionized patch moves into position between stations. The path may last for seconds or for hours, with signals typically being very strong in both directions. Working Es with only a few watts and simple antennas is possible. Most VHF and UHF DXers get their start working Es openings on 6 meters; certainly, more people are actively DXing in that way than in any other.

Aurora

Another large ionized structure in the ionosphere is the aurora, which is oriented vertically instead of horizontally like sporadic E but still reflects signals. When a strong aurora is present, it reflects VHF and UHF signals over a wide area.

One of the neatest things about auroral propagation is that it adds its own audible signature to the signals it reflects. If you’ve ever seen the aurora, you understand how dynamic it is, twisting and shimmering from moment to moment. This movement is even more pronounced for radio waves. The result is that signals reflected by an aurora have a characteristic rasp or buzz impressed on the Morse tone or the spoken voice. A very strong aurora can turn Morse transmissions into bursts of white noise and render voices unintelligible. After you hear the auroral signature, you’ll never forget it.

Tropospheric

Tropospheric propagation (also known as tropo) occurs in the atmospheric layers closest to the Earth’s surface, in an area known as the troposphere. Any kind of large-scale abrupt change in the troposphere, such as temperature inversions or weather fronts, can serve as a conduit for VHF, UHF, and even microwave signals over long distances. If your region has regular cold or warm fronts, you can take advantage of them to reflect or convey your signals.

Tropospheric propagation supports surprisingly regular communications on 2 meters and 1.25 meters, as well as between stations in California and stations on the slopes of Hawaiian volcanoes. A stable temperature-inversion layer forms over the eastern Pacific Ocean most afternoons, so a properly located station on the slope of a volcano at the right altitude can launch signals along the inversion. As the inversion breaks up near land, the signals disperse and are received by mainland amateurs. When conditions are right, mainlanders can send signals back along the same path — more than 2,500 miles!

Meteor scatter

The most fleeting reflectors of all result from the tens of thousands of meteors that enter the Earth’s atmosphere each day, traveling at thousands of miles per hour. The friction that occurs as the meteors burn up ionizes the gas molecules for several seconds. These ionized molecules reflect radio signals, so two lucky stations that have the meteor trail between them can communicate for a short period — a minute or so at maximum. The ionized trails reflect radio waves for shorter and shorter durations as frequency increases. As a result, the lowest-frequency VHF band, 6 meters (50 MHz), is the easiest band for beginners to use for making contacts via meteor scatter.

Hams who attempt to make contact in this way are often called ping jockeys, because the many short reflections off small meteors make a characteristic pinging sound. As you may imagine, ping jockeys go into high gear around the times of meteor showers, large and small. Because of meteor scatter, hams can enjoy meteor showers even during daylight hours.

If you'd like to know more about this unusual mode, check out www.meteorscatter.org.

The most common way to make meteor-scatter contacts is to use the suite of software written by one of ham radio's Nobel Prize winners, Joe Taylor (K1JT). Taylor constructed the free WSJT software program (http://physics.princeton.edu/pulsar/K1JT) to use sophisticated coding techniques, but ordinary hams can use it with no more than a radio and a computer sound card. WSJT is useful for moonbounce (bouncing signals from one station to another off the Moon), meteor scatter, and other difficult communication tasks.

Mountaintopping

What do you do when all the popular DXing methods fail to provide you an over-the-horizon path? Move your horizon! Because VHF/UHF radios are lightweight and the antennas are small, you can drive, pack, or carry your gear to the tops of buildings, hills, ridges, or mountaintops.

The higher the elevation of your station, the farther your signal travels without any assistance from the ionosphere, weather, or interplanetary travelers. Camping, hiking, and driving expeditions can take on a ham radio aspect, even if you’re just taking a handheld radio. From the tops of many hills, you can see for miles, and a radio can see even better than you can. These expeditions are particularly popular in VHF contests. All you have to do is pick up a book of topographic maps, load the car with your radio gear, and head out.

A special award is available for working mountaintop stations. The Summits On the Air (SOTA) program encourages activity by these radio enabled hikers, who often use ultra-low-power gear, which makes contacts with them challenging and fun. You can read up on SOTA at www.sota.org.uk.

Summiits all around BC are registered and ready for your activation. Just searching the SOTA website for the North Okanagan there are 12 summits within an hours drive. Increase your scope to the entire Okanagan Valley and Shuswap region and you probably have more summits than you can visit over 3-5 years of summer summit activity.

Here is a list of the North Okanagan Summits already registered.

Earning VHF and UHF DX awards

Because VHF DX contacts generally aren’t as distant or dispersed as their HF cousins are, VHF DX awards deal with geographic divisions on a smaller scale, called grid squares. Grid squares are the basis for the Maidenhead Locator System, in which one grid square measures 1° latitude by 2° longitude. Each grid square is labeled with two letters (called the field) and two numbers (called the square). Then grid squares are divided even further into subsquares, which are denoted by two additional lowercase letters. My location near Lumby is primary Grid Square DO 00, with the subsquare ‘mf’. Everyone in most of the North Okanagan and Shuswap is in primary grid square DO00, but your subsquare will vary by your home location. Find your grid square by using one of the grid-square lookup site by doing a simple google search for “ham radio gridsquare”.

In North America, where countries tend to be large, the primary VHF/UHF award program is the ARRL's VHF/UHF Century Club (VUCC; www.arrl.org/vucc). The number of grid squares you need to contact to qualify varies by the band, due to the degree of difficulty. As an example, on the lowest two bands (6 meters and 2 meters) and for contacts made via satellites, contacts with stations in 100 different grid squares are required. The ARRL's Worked All States (WAS) program has a vigorous VHF/UHF audience as well.

In Europe, where more countries are within range of conventional VHF/UHF propagation, many of the HF DX awards have VHF/UHF counterparts. Many of those awards are based on contacting different countries, too.

Finally, what would DXing be without a distance record? On the HF bands, with signals bouncing all the way around the world, the maximum terrestrial distance records were set long ago. In VHF/UHF, though, many frontiers are still left. Al Ward (W5LUA) has put together a VHF/UHF/Microwave record list at www.arrl.org/distance-records, and new records are added all the time. Maybe your call sign will be there one day.